Incorporation of particles as fillers in rubber compositions are well known. The fillers are chosen to enhance certain characteristics of the rubber composition. For example, fillers may be used to enhance stiffness, hardness, modulus and so on.
U.S. Pat. Nos. 5,395,891 and 6,127,488 to Obrecht disclose the use of crosslinked polybutadiene and crosslinked styrene-butadiene copolymers respectively as a type of filler. The benefits of the inclusion of these crosslinked polymer particles is lower hysteresis while the polybutadiene gels also impart improved abrasion resistance and the styrene-butadiene copolymer gels offer improve wet traction.
U.S. Pat. Nos. 6,133,364, 6,207,757, and 6,242,534 to Obrecht et al. discloses a rubber composition comprising a crosslinked elastomer particle and a non-crosslinked elastomer. The crosslinked elastomeric particles are functionalized to impart unique surface reactivity for improved coupling with the non-crosslinked host elastomer as well as the subsequent ability to employ coupling agents other than the conventional sulfur-bridged bis-alkoxy silanes. The benefits of the gels are reported to be lower hysteresis, improved abrasion resistance, and improved wet traction.
U.S. Patent Applications published as US 2002/0007011 and US 2001/0053813 to Konno et al. disclose a rubber composition comprising as essential components a crosslinked polymer particle and a non-crosslinked rubber component. The rubber composition may be used to obtain a vulcanized rubber. The crosslinked polymer particles are intended for use as a filler to provide a rubber composition having good processability and handling performance as well as improved tensile strength and wearing resistance when vulcanized. However, it has been found that the particles disclosed in the Kono et al. application tend to soften at higher service temperatures. The effectiveness of the particles as reinforcing fillers is therefore decreased.